Apparatus for grinding



Sept. 8, 1970 F. o. WlENERT 3,527,419

APPARATUS FOR GRINDING- Orizinal Filed June 16. 1965 2 tsheet i INVENTOR.

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APPARATUS FOR GRINDING Original Filed June 16, 1965 2 Sheets$heet 2 INVENTOR.

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ATTORNEY United States Patent O f APPARATUS FOR GRINDING Fritz Otto Wienert, Lewiston, NY. (394 Roosevelt Ave., Niagara Falls, N.Y. 14305) Application June 16, 1965, Ser. No. 467,187, now Patent No. 3,471,093, dated Oct. 7, 1969, which is a continuation-in-part of application Ser. No. 253,158, Jan. 22, 1963. Divided and this application May 7, 1969, Ser. No. 822,419

Int. Cl. B02c 17/06, 17/16, 17/18 US. Cl. 241-453 11 Claims ABSTRACT OF THE DISCLOSURE Grinding apparatus comprising a vessel with a peripheral wall having a continuous, curved inner surface, a plurality of freely movable griding bodies, and means for imparting centrifugal motion to said bodies. Said inner surface is so shaped that the moving grinding bodies are forced to deviate from a circular path at least once during each orbit.

BACKGROUND OF THE INVENTION This application is a division of copending application Ser. No. 467,187, filed June 16, 1965, and now Pat. No. 3,471,093, issued Oct. 7, 1969, the latter being a continuation-in-part of application Ser. No. 253,158, filed Jan. 22, 1963 and now abandoned.

This invention relates to the grinding of material by means of freely movable grinding bodies and more par ticularly to a novel apparatus for grinding by means of grinding bodies which perform their function while being subjected to centrifugal force.

In common practice grinding by means of grinding bodies is caused by gravitational force. For example, in ball mills the balls are continuously lifted by the mill and grind as they cascade downwardly by gravity. The general disadvantage of such mills is that they require a large amount of power for lifting the balls and that only a portion of the balls effectively provide grinding action at any one time.

It is also common practive to achieve grinding or comminuting by moving a definite number of balls or rolls along a prescribed, fixed circular path at such speeds that they exert pressure on this path as a result of centrifugal force. However, the grinding action thus obtained is small in relation to the size of the apparatus because it takes place only in the limited contact zone between the relatively few balls or rolls and the fixed path in the mill.

It is also known to achieve a grinding action with grinding bodies by subjecting to centrifugal force an indefinite number of such bodies freely movable in regard to each other within a vessel of circular cross section and to move the centrifuged grinding bodies mixed with interspersed material to be ground relatively to one another by means of agitators. This agitation within the mass of centrifuged grinding bodies causes high power consumption and heavy wear of the apparatus as is also the case in other agitator type mills of known design. It is further known to suspend material to be comminuted in a fast moving fluid and utilize the kinetic energy of the fluid for cornminution. However, the power consumption in such fluid'energy mills is likewise high.

It has also been suggested to centrifuge grinding bodies with interspersed material against the inner peripheral wall of a rapidly rotating, circular container while simultaneously shifting the axis of rotation of the container in a circular orbit, thereby causing the grinding bodies and materials to vibrate against said wall and comminute the interspersed material.

The present invention avoids the drawbacks of the' above-mentioned previously known and suggested grinding methods and apparatus by repeatedly circulating at high speeds a mass of freely movable grinding bodies interspersed with material to be ground in continuous, curved, non-circular paths. More specifically, the grinding bodies and material are caused to move at high speeds, under the influence of centrifugal forces in closed-curved paths within a generally round (including elliptical) preferably stationary vessel, said paths being along the inner peripheral wall of said vessel and each of said paths having at least a portion thereof in which the radius of curvature varies.

SUMMARY OF THE INVENTION The foregoing is achieved in an apparatus which comprises a preferably stationary vessel having a generally round circumferential or peripheral wall with a continuous, curved inner surface. The vessel contains a number of freely movable grinding bodies and means to impart centrifugal motion to said bodies and the material to be ground so that the bodies race around said curved inner surface. The cross section of the inner peripheral wall of the vessel in an orbital plane, i.e., a plane incorporating the path of a grinding body in such motion, deviates from a circle in at least one place so that the moving grinding bodies are forced to deviate from a circular path at least once during each orbit. Stated more generally, the radius of curvature of the continuous, curved path of each of the grinding bodies in its orbital motion varies at least once in each orbit.

SHORT DESCRIPTION OF THE DRAWINGS In the accompanying drawings, which illustrate prefered embodiments of the invention and some of the possible modifications thereof:

FIG. 1 is a longitudinal sectional view through one type of horizontal mill according to the invention;

FIG. 2 is a cross-sectional view taken approximately on line 2-2 of FIG. 1;

FIGS. 3 and 4 are cross-sectional views similar to FIG. 2 illustrating modified forms of the apparatus illustrated in FIGS. 1 and 2;

FIG. 5 is a longitudinal sectional view through another type of horizontal mill;

FIG. 6 is a longitudinal sectional view through one type of vertical mill according to the invention;

FIG. 7 is a perspective view of a modified type of impeller; and

FIG. 8 is a sectional view of a vertical type mill ac cording to the invention in which orbital movement of the grinding bodies is produced by fiuid streams.

DESCRIPTION OF THE PREFERRED Referring to the embodiment illustrated in FIGS. 1 and 2, the mill casing, comprehensively designated as 11, comprises a horizontal cylindrical body 12. The body 12 is provided with ends 13 and 14 which may be joined to the body portion by welding or other suitable means. The casing 11 is supported on stands 15. Extending axially through the casing 11 and the packing glands or seals 16 on the ends 13 and 14 of the body is an impeller shaft 18 which is rotatably supported exteriorly of the casing by pedestals 19 and which has secured on one end thereof a gear 20 that may be engaged by rotating means (not shown) for said shaft.

In the upper portion of the casing 11, adjacent to the end 14 thereof, an inlet 21 is provided for introducing into the mill grinding bodies and material to be ground. The inlet 21 projects outwardly, preferably tangentially to the body 12, and is so disposed that material or grinding bodies entering the mill therethrough are moving in the same direction as the material and grinding bodies therein. Adjacent to the other end of the casing 11, in the bottom portion thereof, is an outlet 22 therefrom which is provided with a removable screen or grate 23. Within the casing 11 and spaced longitudinally at intervals therein are a plurality of partitions 25 secured to the body 12 in suitable manner, such, for example, as by welding, and each is provided with a center hole 26 around the shaft 18 and a plurality of smaller perforations 27. The latter are sufliciently numerous and of such size as to permit passage of material that is being ground but are not large enough to permit the passage of grinding bodies.

Along the portion of the shaft 18 within the casing 11 a plurality of impellers 28 is provided at spaced intervals. Each of the impellers comprises a double ended yoke 29 mounted on the shaft 18 and secured thereto by suitable means such as a pin 30 so that the bifurcated ends of the yoke extend radially on opposite sides of the shaft. A paddle 32 is pivotally mounted in each of the ends of the yoke 29 on a pin or shaft 31 which extends parallel to the shaft 18. The paddles on each yoke are thus capable of swinging motion or oscillation in the same plane in which they are rotated but around centers radially removed from the axis of rotation. The outer, free ends of the paddles 32 are preferably enlarged, as at 34, longitudinally of the mill casing to increase their striking areas. Adjacent yokes 29 are preferably secured to the shaft 18 at different angles as shown in FIGS. 1 and 2. Also, as will be seen, the interior of the casing 11 is divided into a plurality of longitudinally arrayed, communicating compartments 35a, 35b, 350, by the partitions 25 and a plurality of impellers 28 is located within each of said compartments.

Within each of the compartments 35a, 35b, and 350 there are secured to the body 12, at diametrically opposed positions, as best shown in FIG. 2, a pair of crescentshaped orbit deflectors 36 which extend longitudinally of the body 12 for substantially the full length thereof. The length of the paddles 32 is such that the impellers may revolve within the compartments at high speeds without direct interference from the deflectors. The deflectors may be secured to the wall of the casing by suitable means such as bolts or studs (not shown).

The numeral 40 in FIG. 1 indicates grinding bodies, for example balls of any suitable hard material, which are used in grinding mills according to the invention. It is preferred to have the bodies of different sizes and/ or weights. The number of grinding bodies employed may vary. It is desirable to have enough, as shown in FIG. 1, to at least substantially cover the interior peripheral surface of the mill body 12 when the bodies are moving in orbital paths and enough may be used to provide a layer equivalent in thickness to about one-half the radius of the mill body when they are distributed uniformly around the interior surface of the body 12. In some cases the numbers and/or sizes of grinding bodies in the several compartments 35a, 35b, 350, may be different. The materials used for such bodies may also be different.

In the operation of the mill illustrated in FIGS. 1 and 2 a plurality of hard grinding bodies such as balls 40 are placed in the compartments of the mill and the impeller shaft 1 8 is rotated rapidly by suitable means (not shown) engaging the gear 20 thereon. The revolving paddles 32 of the impellers 28 impart centrifugal motion to all of the balls 40 and thereby cause them to race along the inner curved surface of the mill body and over the deflector 36. The material to be ground is introduced through the inlet 21 and is likewise thrown outwardly by the paddles 32 towards the inner surface of the mill body where it is interspersed in and moves with the balls 40. Because of their different velocities and/or masses, the balls 40 shift their relative positions as the radii of curvature of their orbital paths are changed in passing over the deflectors 36. The shear friction between the balls 40 resulting from such changes in relative position comminutes the interspersed material. Obviously the impellers do not directly contact all of the grinding bodies at any one instant but it will be apparent that because of close contact and friction between the bodies all of them will be moved simultaneously rapidly and repeatedly in closed-curve paths.

OTHER EMBODIMENTS In FIG. 3 there is illustrated a modification of the mill shown in FIGS. 1 and 2. The modification consists in forming the orbit deflectors as curved wedges 42 that gradually increase in thickness in the direction of travel of the mill contents and have their trailing ends steeply inclined toward the inner face 44 of the mill body from the points 43 on the faces of the wedges.

The operation of the modified mill illustrated in FIG. 3 is similar to that of the mill illustrated in FIG. 1 except that the grinding balls adjacent the continuous, curved inner surface of the body 12 upon passing over the points 43 on the faces of the wedge deflectors 42 are caused to jump to the inner face 44 of the body. The distance travelled from the take-off points 43 before striking the face 44 will vary with the mass and the velocity of the balls but in any event the balls in the mass of grinding bodies will move relatively to each other thereby comminuting the interspersed material.

FIG. 4 illustrates further possible modifications of the mill shown in FIGS. 1 and 2. Here the mill body 46 is constructed with diametrically disposed longitudinal troughs 47 and 48 and a third longitudinal trough 57 intermediate them, all of which project outwardly from the main cylindrical portion of the body. As the grinding balls in their orbital paths around the inner wall of the body 46 reach the edge 49 of the trough 47 they will momentarily be out of contact with the wall, but centrifugal force will cause them to move outwardly so that they strike the inner face of the trough while continuing their orbital motions. Then, on reaching the other edge 50 of the trough "47, the balls adjacent the curved inner surface of the body 46 will again be caused to jump before again contacting the inner wall of the cylindrical portion of the body 46.

A liner or filler plate 52 is provided in the trough 48. The plate, which may be secured to the body 46 by suitable means such as bolts or studs (not shown) is so shaped as to modify the deflecting action of the trough on the grinding balls in the mill in their orbital paths. As the outer balls reach the point 53 at the leading edge of the depression 54 formed in the liner 52, they take off, i.e. jump, before striking the inner surface of the liner. However, the trailing edge '55 of the liner 52 has a smooth transition into the curve of the inner face of the cylindrical body portion and, accordingly, the balls are not caused to jump or shift positions abruptly when they leave the trough 48. The trough 57 is similar in structure and action to the trough 47. However, either of the troughs 47 and 57, or both, may be provided with a liner like the liner 52 of trough 48, if desired. The troughs 47, 48 and 57 in this embodiment constitute orbit deflectors for the grinding balls used therein.

In the operation of the modified form of mill illustrated in FIG. 4, as in the embodiments previously described, the orbital paths of the grinding balls will vary in accord ance with their velocities and masses, thus producing shifting of the relative positions of the balls. As previously pointed out, such shifting results in effective grinding of the interspersed material.

It will be understood that in the modified forms shown in FIGS. 3 and 4, as Well as in the embodiment of the invention illustrated in FIGS. 1 and 2, partitions may be employed to divide the mill longitudinally into compartments. In the embodiment of FIG. 4 it will usually be more convenient for the troughs to run for the full length of the mill body, but this is not essential. As in the mill illustrated in FIGS. 1 and 2, in use the mills of FIGS. 3 and 4 should contain at least enough grinding bodies to substantially cover the surface of the inner peripheral wall of the mill and may contain enough bodies to provide a layer equivalent in thickness to about one-half the radius of the mill body when they are distributed uniformly around said wall.

It will be apparent that considering the possible variations in such factors as mill size, ball sizes and weights, percentage of loading feed rate, etc., etc., and the fact that the movements in any grinding mill are inevitably quite complex, it is not feasible to specify a particular deflector shape and/or size as being most efficient. Since the efiiciency in a particular case will depend on many variables, the best arrangements and operating conditions will necessarily be determined by practical use. It should be noted, however, that corners and sharp bends leading to violent impacts of the grinding bodies on the face of the mill body or on each other are preferably avoided since such impacts increase wear and produce indiscriminate impact grinding. For this reason, the mills illustrated in FIGS. 3 and 4 are only intended to be used with the impellers rotating in the direction indicated by the arrows, designed 58 in FIG. 3. Orbital movement of the grinding balls in the opposite direction would result in violent impacts against the back faces of the wedges '42 in FIG. 3 and against the front edge of the depression 54 in FIG. 4.

Still another form of horizontal mill according to the present invention is illustrated in FIG. 5. In this embodiment the mill comprises a casing having a body portion 61 and ends 62 and 63. The casing is generally frustoconical in shape and is provided with an inlet 64 in its upper portion adjacent the smaller end 63 and an outlet 65 in its lower portion adjacent the larger end 62. A removable grate or screen 66 is provided for the outlet 65.

Extending longitudinally through the body portion 61 and projecting through the ends 62 and 63 is a rotatable impeller shaft 67 to which are secured, as by pins 68, a plurality of impellers 69 spaced along the length of the shaft. The impellers 69 are substantially like the impellers 28 in FIGS. 1 and 2, except that, because of the shape of the casing 61, they are graduated in length, the length incerasing toward the large end of the casing. A longi tudinal trough 71 similar to the trough 47 in FIG. 4 is provided along the side of the body 61 to serve as an orbit deflector for the grinding balls 73. The latter are shown distribtuted around the inner periphery of the body approximately as they would appear during operation at some instant.

In operating the mill illustrated in FIG. 5, a sufiicient number of grinding balls are placed in the mill so that the balls are thrown outwardly by the rotating impellers and travel in an orbital path around the inner curved face of the body 61. The material to be ground is introduced through the inlet 64 and becomes interspersed in the mass of grinding balls where it is comminuted by the relative movement between the balls that results from the orbit deflector 71.

As with the mills illustrated in FIGS. 1-4, it is preferred to have the grinding balls in the mill shown in FIG. 5 vary in size and/or mass since the deviations, produced by the deflecting trough, from the normal orbital path of such a mixture of balls will be such that greater grinding efliciency is obtained. Because of the frustoconical shape of the mill casing in FIG. 5 there will, of course, be a tendency for a greater number of the grinding balls and the balls of greatest mass to collect in the portion of larger diameter near the outlet 65. As a result, the grinding or comminuting effect is progressively greater as material to be ground moves from the inlet 64 to the outlet 65. The inlet 64 is preferably arranged so that material enters the mill substantially tangentially, in the direction in which the balls 73 are travelling (see arrow 74), thus preventing ejection of the balls or material.

In the use of apparatus of the type described above, the grinding or comminuting operation is preferably a continuous one with material being fed into the mill adjacent one end and being discharged adjacent the other end. Depending upon the size of the orifices in the discharge grate or screen, all of the feed material may be discharged as it reaches the outlet or only the finer particles may be discharged.

FIG. 6 illustrates an embodiment of apparatus according to the invention in which the orbital paths of the grinding bodies tend to lie in horizontal planes and the general direction of travel of material through the mill is vertical. In this figure the mill casing 77 comprises the generally cylindrical mill body 78, which is provided with a top 79 in which there is an inlet chute 80, and is con structed at its lower end to form a discharge hopper 81 having an outlet 82. A plurality of vertically spaced horizontal partitions 84 are provided within the body 78 to divide the mill into a plurality of compartments 85a, 85b, 850. The partitions 84 are provided with holes or perforations 86 of such size that particles of material may pass through, but the grinding bodies 88 in the several compartments will not pass.

A rotatable impeller shaft 90 extends vertically through the casing 77 and the partitions 84 and carries, securely mounted thereon, as by pins 91, within each of the compartments 85 at least one impeller 92 which may be, as shown, merely a straight bar or may be similar to those illustrated in FIG. 1.

In operation, the impellers 92 when revolved rapidly by rotation of the shaft 90 engage the grinding balls 88 in each compartment and impart to them centrifugal motion that results in orbital movement around the inside face of the body 78. As shown in FIG. 6, the balls 88 are shown distributed approximately as they would be at some instant during their orbital movements. The balls are deflected at least once during each orbit by a deflector associated with the casing such as the vertical, longitudinally extending trough 94. Trough 94 may be constructed substantially like the trough 47 in FIG. 4 and functions in the same way. As in the previously described embodiments, the grinding balls 88 are preferably of different sizes and/or masses to increase the grinding effect. The holes 86 in one or all of the partitions 84 may be of such size that the material to be ground is retained in a compartment until it is reduced to a desired degree of fineness before it can pass to the next compartment or to the discharge hopper.

FIG. 7 illustrates an alternative form of impeller which may be used in carrying out the invention. As shown this comprises a plate 96 to which are secured a plurality of vertically extending vanes 97. The vanes which may be spiral, as shown, or straight if desired, extend from the collar 98 provided for attachment to a shaft to the periphcry of the plate and are adapted to engage the grinding balls and project them into obital paths within a mill. The plate 96 is provided with a plurality of perforations 99 to permit passage of material particles and, when used in a mill like the one illustarted in FIG. 6, may serve as a partition as well as an impeller. Also, in such a mill, impellers of this type facilitate starting. When employed in a horizontal mill, impellers of this type may be provided with vanes on both sides of the plate 96.

FIG. 8 illustrates, somewhat diagrammatically, a modified form of mill according to the present invention in which the grinding bodies such as the balls 102 have an orbital motion imparted thereto by fluid jets or streams. The mill in this embodiment comprises a stationary casing, generally designated by the numeral 103, having a vertical, cylindrical body 104, the bottom 105 of which is dished inwardly to cause grinding balls 102 resting thereon to roll toward the side of the mill. The top 107 of the body has an upwardly projecting discharge duct 108 and concentric therewith is an inwardly projecting inlet tube or chute 109. A plurality of tangentially disposed nozzles 111 are provided around the side of the body 104 for admitting fluid, preferably compressed air or high pressure steam, to the interior of the mill.

The operation of the mill illustrated in FIG. 8 is somewhat similar to that of a cyclone. The fluid jets entering through nozzles 111 impart centrifugal motion to the balls 102, the latter being shown approximately as they would appear in operation at some instant, and to the material being ground which is introduced through the inlet tube 109 and interspersed with the balls. The relative movement of the balls in their orbital movement, increased by the orbital deflectors 112, which extend longitudinally in the body 104 and may be constructed substantially like the deflectors 36 of FIG. 1 or 42 of FIG. 3, comminutes the interspersed material until it is fine enough to be swept out of the mill through the outlet duct 108 by the spent fiuid. Thus, the mill also acts as a classifier. If desired, a similar mill with the grinding bodies moved by fluid streams or jets in orbital paths in substantially vetrical planes could be provided.

It will be understood that the mills shown in FIGS. 5, 6 and 8 will be provided with suitable supporting means and that in the two former mills suitable means will be provided for rotation of the shafts 67 and 90. Also in FIG. 8 the discharge duct 108 will be connected to a suitable hopper, classifier, or the like, and the inlet chute will be connected to a feed hopper or the like. It will be further understood that mills according to the present invention may be formed of any suitable material and may be provided with such conventional adjuncts (not shown) as inspection and/ or filling holes, linings, packing glands, and the like. Also, they may be of any desired and feasible size.

As has ben indicated above, many modifications of and variations in the structure of mills according to the present invention are possible. For example, the number of orbital deflectors employed may vary as neccessary or desirable and the type or types of deflector used may also be varied. Thus, if desired, a defletcor such as that shown in FIGS. 1 and 2 might be used in the construction illustrated in FIG. 4 instead of one or more of the troughs. The construction of and number of impellers used is also subject to change in accordance with circumstances, and such impellers may, as desired, be disposed at varying angles one from another, as suggested in FIGS. 1 and 5, or parallel, as shown in FIG. 6. It may be noted here that pivoted impellers such as shown in FIG. 1 are advantageous in starting with a loaded mill since they gradually exert more force as their speed increases and thus do not pick up the whole load at once.

In many cases the use of partitions to separate the mill into compartments is desirable since this permits the use of graduated ball sizes in the several compartments and thus increases efliciency. The number of partitions, their spacing, the number of impellers in each compartment, and the type and number of orbit deflectors used in such compartments is a matter of choice. However, under some conditions it may be desirable to have the mill body comprise only a single compartment so that both the balls and material to be ground may be simultaneously introduced after the impellers are revolving. The starting load of the mill may thus be minimized. If desired'in such cases,

there may be recirculation of grinding bodies with con-' tinuous feed and discharge thereof.

The new method of grinding described herein offers the advantage of allowing preferential grinding, as for instance, when it is desired to liberate hard material from soft material by the least amount of comminution. Such preferential grinding may be achieved according to the new method by choice of rotational speed of the impellers, the extent of the diversion from the circular path, the frequency of diversion during one orbit, and the number, size, specific density, and distribution of the grinding bodies. The new method is suitable for preferential grinding because it does not involve indiscriminate heavy impact, as in tumbling ball mills, or forceful shear under high pressure as in mills with a fixed path for a grinding element or with agitators stirring a bed of balls.

The grinding operation, according to the method of the invention, is preferably continuous and the finished ground material may be separated in the mill and discharged continuously, or the material may be discharged continuously, separated outside the mill into the desired fine material and coarser particles, the latter being returned to the mill for further grinding. It is understood that in preferential grinding the coarses particles may be the desired product so that the fines are discarded in such a case. The finely ground material may be separated in the mill and discharged from it by means of a current of air or other gas or fluid. The grinding may be either dry or wet.

I claim:

1. Apparatus for grinding which comprises an elongated, stationary casing having end walls and a circumferential wall formed with a continuous, curved inner surface; a mass of freely movable grinding bodies in said casing;'a rotatable shaft extending longitudinally through said casing; and a plurality of impellers carried by said shaft and arranged longitudinally thereof adapted to engage said grinding bodies and impart simultaneously to all of said bodies rapid and repeated centrifugal motion in closed curved paths along said curved inner surface, said surface being so shaped that the radius of curvature of each of said paths is variable through at least a minor portion thereof.

2. Grinding apparatus as defined in claim 1 in which said rotatable shaft extends vertically.

3. Grinding apparatus as defined in claim 1 in which said rotatable shaft extends horizontally.

4. Grinding apparatus as defined in claim 1 in which said curved inner surface is essentially round in cross section.

5. Grinding apparatus as defined in claim 1 in which said curved inner surface is essentially elliptical in cross section.

6. Grinding apparatus as defined in claim 1 in which said inner surface includes, extending parallel to said shaft, at least one orbit deflector for said bodies.

7. Grinding apparatus as defined in claim 2 in which said inner surface includes, extending parallel to said shaft, at least one orbit deflector for said bodies.

8. Grinding apparatus as defined in claim 4 in which sald inner surface includes, extending parallel to said shaft, at least one orbit deflector for said bodies.

9. Grinding apparatus as defined in claim 2 in which sa1d curved inner surface is essentially round in cross section and includes, extending parallel to said shaft, at least one orbit deflector for said bodies.

10. Grinding apparatus as defined in claim 9 in which said caslng 1s separated into a plurality of compartments.

11. Grmd ng apparatus as defined in claim 10' in which there are grmding bodies in each of said compartments and at least one impeller is provided in each compartment.

References Cited UNITED STATES PATENTS 927,516 7/1909 Emerick 241-153 2,931,584 4/1960 Fairchild 241-153 3,008,657 11/1961 Szegvari 241 3,018,059 1/1962 Lodige 241-172 X 3,149,789 9/1964 Szegvari 241172 X FOREIGN PATENTS 440,089 2/ 1927 Germany.

489,223 1/ 1930 Germany.

489,327 1/ 1930 Germany.

LESTER M. SWINGLE, Primary Examiner D. G. KELLY, Assistant Examiner US. Cl. X.R. 241-174, 179 

